On 25/01/2011, at 12:48 PM, Aaron Riemer wrote: > This is a really basic question and I should know the answer. I am just > pondering over loop guard and UDLD and take this for example:
note that at a fundamental level, mechanisms in Spanning Tree are always going to be different to those that work on physical ports. for example, if you had a port-channel (LAG bundle) of 4 physical member interfaces and ran STP over that, how many of those interfaces in the bundle would be moving BPDUs? answer: 1. this should show quite clearly why mechanisms such as UDLD are important. > Two switches are connected via a pair of fibre. Now let's say the TX path > from switch1 (RX on switch2) fails or is disconnected but the other fibre is > still operational. I would have thought that logically Switch 2 should see > that it is no longer receiving "light" on its RX path and bring the port > down? yes, swltch 2 would consider the interface to be operationally down (loss of light). switch 1 is still receiving light. > > > > Obviously this is not the case. it should be. > Therefore my question is what determines if > a port is physically "UP"? What physical checks are done by the switch port > and how does it determine if media is attached? the PHY/transceiver tells the switch that it has link. cheers, lincoln. _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
